Oscillation generator comprising electron discharge devices



June 8, 1937. a. M. WRIGHT El AL 2,082,813

OSCILLATION GENERATOR COMPRISING ELECTRON DISCHARGE DEVICES Filed 001?.8, 1955 ATTORNEY Patented June 8, 1937 OSCILLATION GENERATOR COMPRISINGELECTRON DISCHARGE DEVICES George Maurice Wright and Nol'Meyer Rust,Chelmsford, England, assignors to Radio Corporation of America, acorporationof Dela- Application October 8, 1935, Serial No. 44,046

In Great Britain August 30, 1934 2 Claims. (01. 250-36) t N Thisinvention relates to electrical oscillation generators comprisingelectron discharge devices and more particularly to tuned thermionicvalve oscillation generators of the kind wherein a thermionic valve isconnected in a reaction circuit for self-oscillation, i. e., isconnected so that its output electrode is back coupled to its input orcontrol electrode for the generation of sustained oscillation.

Known oscillation generators of this kind vary the frequency of thealternating current generated when. the intensity of the reactioncoupling is varied. Such inconstancy of frequency is often undesirablesince changes in the reaction intensity made for the purpose of securingthe best operation of the generator itself ,or that of associatedcircuits, result in a frequency change which may mask the effect aimedat in making such adjustments. i

The reason for such variation in frequency is that the coupling betweenthe portions of the circuit providing the reaction results in amodification of the effective electrical constants of the path of theoscillatory current, and so when the coupling is varied, the frequencyof the generated oscillations is correspondingly changed.

The invention is explained in connection with Figs. 1 and 2 of thedrawing. Fig. 1 represents an example of the prior art and Fig. 2 showsthe present improvement thereoven As an example, known oscillationgenerators of the kind referred to may, for the purposes of the presentinvention, be regarded as typified by that well known oscillator circuitarrangement illustrated in the accompanying Fig. 1, wherein the anodecircuit of a triode I is back coupled to its control grid 2 through anadjustable coupling condenser 3 connected between the said control grid2 and the adjacent end! of a parallel tuned anode oscillatory circuit 4,5, anode potential from a source (not shown but having its positiveterminal marked +HT) being applied to the anode 6 through a tapping 1 onthe inductance 4 in the parallel tuned circuit 4, 5, and the controlgrid 2 being connected to the cathode 8 through a grid leak 9 thecathode being, of course, connected to the negative terminal -HT of theanode potential source.

Now, with this and with similar oscillator circuit arrangements, theintentions are that the frequency of the oscillations generated shall bedetermined by adjusting the natural frequency of the paralleltunedcircuit 4, 5,-the condenser 5 in this tuned circuit is generallymade variable for this purpose-and the energy feed back shall tude.

be determined by adjusting the coupling condenser 3. However, if thecircuit of Fig. 1 be analyzed, it will be seen that thecoupling con,-

denser 3 is in series with the grid-anode selfcapacity of the valve I,"and that these two series connected capacities are together. in parallelwith the parallel tuned circuit 4, 5. Accordingly, although it isintendedthat the frequency generated shall be determined onlyby theadjustment of the parallel tuned circuit 4, 5, and the reactioncondition be determined only by the adjustment of the coupling condenser3, in fact any adjustment of the coupling condenser will alter thefrequency generated since this condenser (in series with the grid-anodeself-capacity of the valve) is in shunt across the parallel tunedcircuit. This interdependence of the adjustment means provided forcontrol of the reaction conditions and control of the frequency is, inpractice, very undesirable and the main object of the present inventionis to provide an improved thermionic oscillation generator of the kindreferred to, wherein adjustment of the conditions for oscillationgeneration can be made substantially without altering the frequencygenerated.

It can also be shown that other known types of reaction arrangementmanifests similar modifications of the constants of the oscillatorycircuit.

According to this invention, the valve employed in a thermionicoscillation generator of the kind referred to, is of the so-calledvariable mu type, and adjustment of the reaction conditions is effectedsubstantially without affecting the frequency generated by adjusting anamplification determining potential applied to an electrode of thevalve, the hitherto usual variable coupling condenser in the reactioncircuit being replaced by a fixed coupling condenser or other reactiondevice or arrangement of predetermined. magni- One arrangement inaccordance with this invention is shown in the accompanying Fig. 2. Herethe oscillator valve la is of the "variable mu type and has its anode 6aconnected to its control grid 2a through a parallel tuned circuit 4, 5,which is connected at one end to said anode 6a and at the other end isconnected through a fixed coupling condenser 3a to the control grid 2a.The control grid is connected to one end of a choke Ill whose other endis connected to a variable tapping point ll upon a potentiometerresistance l2 which is shunted by a bias potential source 13. One end ofthe potentiometer resistance I2 is connected to the valve cathode 8a towhich point the negative terminal of the anode potential source is alsoconnected, the positive terminal of this source being connected to atapping point 1 upon the inductance 4 in the parallel tuned circuit. Thechoke H) which 5 is a high frequency choke, serves to prevent thepotentiometer producing a high frequency short circuit path between thecontrol grid and the cathode. The tendency of the system to oscillate isadjusted by moving the potentiometer tapping point H upon thepotentiometer resistance l2 and obviously this adjustment varies thegrid bias for the valve, and, in a variable mu type of valve the gridbias potential'is 'an amplification determining potential. It will beappreciated accordingly that in this improved circuit arrangementvariation of the position of the potentiometer tapping point i I willadjust the reaction conditions substantially without altering thefrequency of oscillation.

Any suitable known type of variable mu valve can be employed in carryingout this invention, a convenient and commonly available type being thatwherein the grid is constituted by an approximately helical wire Windingwhose pitch is not constant but varies over the length of the grid.

What we claim is: 1. An oscillation generator for generating continuous,uninterrupted oscillations of substantially constant frequencycomprising an electron discharge device of the variable mu type havingan anode, cathode and a grid, said device being characterized by agradual variation of mutual conductance over a wide range with variationin the bias potential applied to said grid, a frequency determiningnetwork coupled between said anode and grid, means for applying asuitable bias potential to said grid and for manually varying said bias,whereby the mutual conductance of said device is varied without varyingthe frequency generated by said oscillation generator.

2. An oscillation generator for generating continuous, uninterruptedoscillations of substantially constant frequency comprising an electrondischarge device of the variable mu type, having an anode, cathode andgrid, said device being characterized by a gradual variation of mutualconductance over a wide range with variation in the bias potentialapplied to said grid, a feedback circuit including frequency determiningmeans connecting said anode and grid, a choke coil and a variableresistance in series between said grid and cathode, whereby the mutualconductance of said device can be adjusted by means of said variableresistance without varying the frequency generated by said device.

GEORGE MAURICE WRIGHT. NOEL MEYER RUST.

